RE: [PATCH v2 11/35] x86/bugs: Restructure spectre_v1 mitigation

[Kaplan, David]

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
> Sent: Thursday, November 14, 2024 12:57 AM
> To: Kaplan, David <David.Kaplan@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Borislav Petkov <bp@xxxxxxxxx>; Peter
> Zijlstra <peterz@xxxxxxxxxxxxx>; Josh Poimboeuf <jpoimboe@xxxxxxxxxx>; Ingo
> Molnar <mingo@xxxxxxxxxx>; Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>;
> x86@xxxxxxxxxx; H . Peter Anvin <hpa@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2 11/35] x86/bugs: Restructure spectre_v1 mitigation
>
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> On Tue, Nov 05, 2024 at 03:54:31PM -0600, David Kaplan wrote:
> >  static void __init spectre_v1_select_mitigation(void)
> >  {
> > -     if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1) || cpu_mitigations_off()) {
> > +     if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1) ||
> > + cpu_mitigations_off())
> >               spectre_v1_mitigation = SPECTRE_V1_MITIGATION_NONE;
> > +}
> > +
> > +static void __init spectre_v1_apply_mitigation(void) {
> > +     if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1) ||
> > +cpu_mitigations_off())
>
> We probably don't need to repeat this check, is this okay:
>
>         if (spectre_v1_mitigation == SPECTRE_V1_MITIGATION_NONE)
> >               return;
> > -     }
> >
> >       if (spectre_v1_mitigation == SPECTRE_V1_MITIGATION_AUTO) {

I don't think so.  That would stop us from printing the message about the system being vulnerable at the end of the function.

We should only not print the message I believe if the CPU is actually not vulnerable or mitigations are globally disabled.  Although now I realize my patches may not be suppressing the print statements always if cpu_mitigations_off(), so I need to go and fix that.

--David Kaplan